Polymer Matrix Particles For Inhibitingscale Formation In Oil And Gas Wells

ABSTRACT

Polymer matrix particles useful for inhibiting scale formation in oil and gas wells are described. The insoluble, porous, crosslinked polymer matrix includes a polymer backbone and ionic functional groups covalently bonded to the backbone, the ionic functional groups being capable of selectively attracting and binding salt scale-forming ions when in contact with a liquid containing such ions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority to U.S. Provisional Application No.62/381,839 filed Aug. 31, 2016, the entire disclosure of which isexpressly incorporated herein by reference.

BACKGROUND OF INVENTION

This invention relates in general to materials useful in oil and gasproduction, and in particular to improved materials for inhibiting scaleformation in oil and gas wells.

Oil and gas production usually involves drilling wells to extract theoil and gas from underground formations. The extracted oil and gas oftenis accompanied by brine. As the brine proceeds through the well from theformation to the surface, pressure and temperature change and waterevaporates, and dissolved salts can precipitate and form scale onsurfaces of the well and related equipment. Scaling can also result fromthe practice of brine injection into a formation to maintain pressureand sweep the oil and gas to producing wells. Some common oilfieldscales are halite, calcite, barite, celestite, anhydrite, gypsum andiron sulfide.

The formation of scale on surfaces of the well and related equipment isa major production problem. Scale build-up reduces well productivity andshortens the lifetime of production equipment.

A number of methods can be used for removing scale after it has formed,including milling, fluid jetting, and chemical dissolution. However, inorder to clean the well and equipment it is necessary to stop theproduction, i.e., by killing/stopping the well, which is time-consumingand costly. Also, these methods are not always effective.

Other methods can be used for inhibiting scale formation. For example,fresh water can be pumped into the well as a diluent to reduce saltprecipitation from the brine. However, the fresh water is not only aprecious natural resource, but it also represents a significant processcost because typically it must either be shipped to the drilling site orproduced on-site using desalination equipment.

Scaling can also be reduced by the introduction of scale inhibitors intothe formation or well. Some commercially available halite inhibitors usepolymeric peptide features. An example is Bellasol® H21, manufactured byBWA Water Additives, Tucker, Ga., USA.

There is still a need for improved materials for inhibiting scaleformation during oil and gas production.

Ion-exchange resins are used in different separation, purification anddecontamination processes, such as water softening and waterpurification. For an overview see Alexandratos, Spiro D. Ion-ExchangeResins: A Retrospective from Industrial and Engineering ChemistryResearch, Ind. Eng. Chem. Res. 2009, 48, 388-398.

The patent literature discloses preparing quaternary ammonium salts frompolymerizable tertiary ammonium monomers: see U.S. Pat. No. 4,179,549 byBuriks et al., issued Dec. 18, 1979.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic illustration of a polymer matrix particleaccording to the invention removing salt scale-forming ions from brineinside a well to inhibit scaling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to polymer matrix particles for inhibitingscale formation in oil and gas wells. The technology provides a numberof advantages in effectiveness and cost savings, and addresses theproblem of water usage in oil and gas production. Moreover, theinhibition mechanism of the matrix particles will work in a large rangeof pH values commonly encountered in drilling operations.

Although there are scale inhibitors currently in use in the oil and gasindustry, the present invention offers a new mechanism to inhibit scaleformation. Current scale inhibitors such as hydroxyethylenediphosphonicacid (HEDP) and diethylenetriaminepenta (methylenephosphonic) acid(DTPMP) work by using chelation to attract positively charged metal ionspresent in brine. After the metal ions are chelated, their salts cannotform because the ions are more strongly covalently bonded to thechelating molecule than attracted to anions in the brine.

Unfortunately, the current scale inhibitors are ineffective to inhibitformation of halite and other scales formed by monovalent ions. Forexample, halite crystals are composed of sodium and chloride ions, whichare monovalent. Metal ions are generally divalent (e.g., calcium,barium) and chelation has a higher preference for the more highlycharged metal ions than the monovalent sodium ions. This leaves thesodium ions free to form halite crystals with the chloride ions in thebrine upon cooling or increase in concentration.

In contrast, the polymer matrix particles described herein work by anon-chelating mechanism and are effective for binding either monovalentor divalent ions. Thus, the polymer matrix particles are effective forinhibiting the formation of halite and other scales formed by monovalentions, in addition to scales formed by divalent ions.

The polymer matrix particles are each comprised of a water-insoluble,porous, crosslinked polymer matrix or support structure. The matrix isan amorphous polymer in which the crosslinks provide a three-dimensionalnetwork. The polymer matrix comprises a polymer backbone and ionicfunctional groups covalently bonded to the backbone.

The polymer backbone of the matrix may comprise any suitable polymer orcopolymer. Examples of polymers include, but are not limited to,polyacrylates, polyurethanes, polyesters, polystyrenes, polyamides,polyarylates, poly(phenylene sulfide)s, polysulfones, poly(ethersulfone)s, polyolefins, polyvinyls, poly(vinyl alcohols),polyfluorocarbons, polyethers, polycarbonates, poly(phenylene ether)s,and poly(ether ketone)s.

In certain embodiments, the polymer backbone of the matrix is selectedfrom the group consisting of polyacrylates, polyurethanes, polyestersand polystyrenes.

Examples of polyacrylates include polymethacrylates, poly(alkylmethacrylate)s such as poly(methyl methacrylate)s and poly(ethylmethacrylate)s, and polyacrylonitriles.

Polyurethanes are reaction products of a diisocyanate, a polyol, and,where necessary, a chain extender such as ethylene glycol orethylenediamine. Representative urethane resins are prepared from a softsegment and a hard segment. The soft segment may include, for example, apolyester diol, a polyether diol, or a polycarbonate diol. The hardsegment may include, for example, an isocyanate, a low molecular weightdiamine, or a glycol.

Examples of polyesters include aliphatic polyesters such aspolycaprolactones and poly(lactic acids; and aromatic polyesters such aspoly(ethylene terephthalate)s and polybutylene terephthalate)s.

Examples of polystyrenes include styrenic polymers, copolymers ofstyrene typically with (meth)acrylic acid, a (meth)acrylic ester, oracrylonitrile, and copolymers including a rubber component, such ashigh-impact polystyrene resins and acrylonitrile-butadiene-styreneresins.

The matrix of the polymer matrix particles may be crosslinked in anysuitable manner. For example, monomers suitable to form crosslinks maybe mixed with monomers suitable to form the polymer backbone, and aninitiator, and the mixture polymerized using a free radicalpolymerization process. Other types of polymerization processes may alsobe used.

Some nonlimiting examples of crosslinking monomers include divinylbenzene, vinylbenzyl chloride, glycidyl methacrylate, ethyleneglycoldimethacrylate, ethyleneglycol diacrylate, butanediol dimethacrylate,butanediol diacrylate, hexanediol diacrylate, pentaerythritoltriacrylate, tetraethylene glycol dimethacrylate, trimethylolpropanetriacrylate, isophorone diisocyanate, and trimethylolpropanetrimethacrylate.

Some nonlimiting examples of free radical initiators include azocompounds such as 2,2′-azobisisobutyronitrile (AIBN) andphenylazotriphenylmethane, peroxides such as benzoyl peroxide anddiacetyl peroxide, and ammonium persulfate.

The degree of crosslinking and the porosity of the polymer matrix can beadjusted to optimize its mechanical properties, such as structuralrigidity and swelling behavior, and to optimize ion transport into andout of the particle.

The polymer matrix particles have a tunable particle size. The polymermatrix particles may have any suitable shape. In certain embodiments,the particles are regularly shaped, having a shape such as spherical,spheroidal, elliptical, cylindrical or the like. The particles may bereferred to as “beads”. In other embodiments, the particles areirregularly shaped, having a shape such as angular, amorphous or thelike.

The polymer matrix particles have tunable ion affinity characteristics.The polymer backbone is functionalized with carefully chosen ionicfunctional groups that selectively attract and bind the ions of interestfor inhibiting formation of a particular type or types of scale in oilor gas wells. This allows for a much greater degree of specificity fortargeting a wide range of ionic actors in scale formation.

When injected into the well, the matrix particles act as an ion sponge,attracting the scale-forming ions and thereby preventing crystallizationof the ions from beginning. The functionalized matrix particles aredesigned to have a selective uptake of the scale-forming ions.

The ionic functional groups of the polymer matrix particles are groupsthat are ionizable and associated with ions. When the matrix particlesare injected into a well, the scale-forming ions inside the wellexchange with the ions of the functional groups and are ionically bondedto the functional groups.

Depending on the target scale-forming ion(s), the ionic functionalgroups may be mono- or divalent cationic groups, mono- or divalentanionic groups, or combinations of different groups. The groups may alsobe categorized as strongly acidic, weakly acidic, strongly basic orweakly basic.

Some nonlimiting examples of cationic functional groups include sulfonicacid, phosphoric acid, carboxylic acid, phosphonic acid, monosulfateester, mono- and diphosphate ester groups, hydroxylic groups of phenol,thiol, perfluoro tertiary alcohol groups, and other groups which providea negative fixed charge in aqueous or mixed water and organic solventsolutions.

Some nonlimiting examples of anionic functional groups includequaternary ammonium groups (also referred to as quaternary amines),primary, secondary and tertiary amino groups (amines), tertiarysulfonium groups, quaternary phosphonium groups, and other groups whichprovide a positive fixed charge in aqueous or mixed water and organicsolvent solutions.

In certain embodiments, the ionic functional groups are capable ofselectively attracting and binding the chloride ions and/or the sodiumions commonly present in halite scale. They may also bind other halideions and/or other alkali metal ions. For example, the functional groupsmay be monovalent cationic groups capable of selectively binding halideions such as chloride ions. Alternatively, they may be monovalentanionic groups capable of selectively binding sodium ions. In certainembodiments, the anionic groups are sulfonate groups.

In a particular example, the target ion is chloride, one of the mainactors in salt crystal formation in oil and gas wells. In this case, amaterial such as an acrylic acid monomer that is functionalized with aquaternary ammonium group may be polymerized to prepare thefunctionalized polymer matrix.

As illustrated in FIG. 1, the matrix particles are injected into a wellcontaining ions that form scaling on pipes. The polymer backbone iscovalently functionalized with ionic compounds containing counter ionsfor the target ion. In order to maintain neutrality, the particle willtake up the target ion (chloride is illustrated) to balance out thecharge on the functional group attached to the polymer backbone.

The ionic functional groups are covalently bonded to the polymerbackbone of the polymer matrix. The functionalization may be achieved byfirst functionalizing monomers and then polymerizing the monomers toproduce the polymer backbone. Alternatively, the functionalization maybe achieved by first polymerizing monomers to produce the polymerbackbone and then functionalizing the backbone. Methods offunctionalization of monomers and of polymers are known in the field ofpolymer chemistry.

The degree of functionalization of the polymer matrix may be tuned toachieve a desired thermodynamic equilibrium state of the system (thepolymer matrix particle and the liquid contacting the particle).

In one embodiment, the present invention relates to a suspension forinhibiting scale formation in oil and gas wells. The suspensioncomprises the above-described polymer matrix particles suspended in anaqueous medium. The aqueous medium may be water, or a mixture of waterand other material(s) useful for enhancing the invention or otherwisebenefiting operation of the well.

The invention also relates to a method of inhibiting scale formation.The method comprises injecting the polymer matrix particles into an oilor gas well, so that the particles come into contact with a liquidcontaining salt scale-forming ions. For example, the liquid may be abrine. The ionic functional groups of the polymer matrix particlescontact the liquid and selectively attract and bind the saltscale-forming ions.

The polymer matrix particles may be injected into the well in anysuitable manner. For example, they may be injected in the form of anaqueous suspension of particles as described above. Alternatively, theparticles may be injected without putting them in a suspension. They maybe injected using any suitable equipment.

Further, the polymer matrix particles may be injected at any suitablelocation so that they come into contact with scale-forming ions in thewell. In a production well, this may include injection into the tubing,drill pipe, or casing of the wellbore, or injection into the collectionof pipes and valves on top of the wellbore. In certain embodiments, theparticles may first be injected into an oil or gas formation, forexample through an injection well, before being extracted through aproduction well.

After the polymer matrix particles have been used for inhibiting scaleformation by binding scale-forming ions in the oil or gas well, theparticles may be easily separated and removed downstream by filtrationor gravimetric means. The separated particles may be regenerated forreuse by eluting a controlled pH buffer through a bed of spent particlesto displace the scale-forming ions from the particles.

In an alternative embodiment, the polymer matrix particles areincorporated in a coating that is applied to interior surface(s) of anoil or gas well to inhibit scaling. The coating can have any compositionthat allows the polymer matrix particles to come into contact withscale-forming ions. For example, the coating may have a continuous phasethat is oil-based, such as a vegetable oil, or resin-based. In additionto the polymer matrix particles and the continuous phase, the coatingmay include other treatment chemicals useful in oil or gas wells, suchas corrosion inhibitors.

The polymer matrix particles of the invention provide a number ofadvantages compared to alternative approaches to inhibiting scaleformation in oil and gas wells. Alternative approaches may includedesalinating water on site for use as a diluent to reduce saltprecipitation, or adding scale inhibitors that work by chelation. Theuse of the polymer matrix particles allows for less onsite equipmentcompared to onsite desalination; this technology does not requireadditional equipment on site. The polymer matrix particles are moreeffective than chelating inhibitors for inhibiting scaling caused bymonovalent ions such as halite. The polymer matrix particles providecost and performance advantages to the oil and gas industry.

Certain embodiments of the present invention are defined in the Examplesherein. It should be understood that these Examples, while indicatingpreferred embodiments of the invention, are given by way of illustrationonly. From the above discussion and these Examples, one skilled in theart can ascertain the essential characteristics of this invention, andwithout departing from the spirit and scope thereof, can make variouschanges and modifications of the invention to adapt it to various usagesand conditions.

Examples

The usefulness of the present technology to prevent crystallization ofhalites was demonstrated in the following study. Tetrabutylammoniumbromide (TBAB) was compared to alternative potential saltcrystallization inhibitors: p-toluene sulfonic acid (PTSA), potassiumacetate and a control system with no additive. Each test system wasadded to a supersaturated solution of sodium chloride and allowed to sitovernight. After 24 hours, the TBAB sample was the only vial that didnot show any evidence of salt crystallization. This work is detailedhereinbelow.

Tests to Prevent NaCl Formation

Make a supersaturated NaCl solution and see if additives preventcrystallization of the NaCl.

Test #1: Dissolve 2.5 g potassium acetate (KC₂H₃O₂) in 47.5 g DI water.Add 34.55 g NaCl to make the solution supersaturated. Roll mix for 2hours.

Test #2: Dissolve 50 g NaCl in 125 ml DI water to make a supersaturatedsolution. Roll mix for 2 hours.

Test #3: Dissolve 2.5 g p-toluene sulfonic acid (PTSA) in 47.5 g DIwater. Add 38.55 g NaCl to make the solution supersaturated. Roll mixfor 2 hours.

Test #4: Dissolve 2.53 g tetrabutylammonium bromide (TBAB) in 47.5 g DIwater. Add 36.74 g NaCl to make the solution supersaturated. Roll mixfor 2 hours.

For each of the four test samples, after the roll mixing, use a 0.2 nmsyringe filter to filter out NaCl. Allow the samples to sit to followcrashing out.

24 hours later: 10 crystals appeared in the PTSA system (Test #3) and inthe saturated NaCl system (Test #2), and 5 crystals appeared in theKC₂H₃O₂ system (Test #1). Zero crystals appeared in the TBAB system(Test #4).

About 3 weeks later there was no change in the crystallization comparedwith 24 hours.

All publications, including patents and non-patent literature, referredto in this specification are expressly incorporated by reference herein.Citation of the any of the documents recited herein is not intended asan admission that any of the foregoing is pertinent prior art. Allstatements as to the date or representation as to the contents of thesedocuments is based on the information available to the applicant anddoes not constitute any admission as to the correctness of the dates orcontents of these documents.

While the invention has been described with reference to various andpreferred embodiments, it should be understood by those skilled in theart that various changes may be made and equivalents may be substitutedfor elements thereof without departing from the essential scope of theinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from the essential scope thereof.

Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed herein contemplated for carrying outthis invention, but that the invention will include all embodimentsfalling within the scope of the claims.

What is claimed is:
 1. Polymer matrix particles for inhibiting scale formation in oil and gas wells, each particle comprising a water-insoluble, porous, crosslinked polymer matrix, the polymer matrix comprising a polymer backbone and ionic functional groups covalently bonded to the backbone, the ionic functional groups being capable of selectively attracting and binding salt scale-forming ions when in contact with a liquid containing such ions.
 2. The polymer matrix particles of claim 1, wherein the particles have a tunable particle size.
 3. The polymer matrix particles of claim 1, wherein the polymer matrix has a tunable swelling characteristic.
 4. The polymer matrix particles of claim 1, wherein the crosslinking and porosity of the polymer matrix can be adjusted for tuning of structural rigidity and swelling behavior of the polymer matrix, and to achieve optimal ion transport into the polymer matrix.
 5. The polymer matrix particles of claim 1, wherein the polymer matrix has a degree of functionalization which is tunable to determine a thermodynamic equilibrium state of the particle and the liquid contacting the particle.
 6. The polymer matrix particles of claim 1, wherein the ionic functional groups are mono- or divalent cationic groups.
 7. The polymer matrix particles of claim 1, wherein the ionic functional groups are mono- or divalent anionic groups.
 8. The polymer matrix particles of claim 1, wherein the ionic functional groups are capable of selectively binding halite-forming ions.
 9. The polymer matrix particles of claim 8, wherein the ionic functional groups are monovalent cationic groups capable of selectively binding halide ions.
 10. The polymer matrix particles of claim 9, wherein the monovalent cationic groups are quaternary ammonium groups.
 11. The polymer matrix particles of claim 9, wherein the halide ions are chloride ions.
 12. The polymer matrix particles of claim 8, wherein the ionic functional groups are monovalent anionic groups capable of selectively binding sodium ions.
 13. The polymer matrix particles of claim 12, wherein the monovalent anionic groups are sulfonate groups.
 14. The polymer matrix particles of claim 1, wherein the particles are regular in shape.
 15. The polymeric matrix particles of claim 1, wherein the polymer backbone of the polymer matrix is selected from the group consisting of polyacrylates, polyurethanes, polyesters and polystyrenes.
 16. The polymeric matrix particles of claim 1, wherein the polymer matrix has a polyacrylate backbone, and wherein the ionic functional groups are quaternary ammonium groups capable of selectively binding chloride ions.
 17. A suspension for inhibiting scale formation in oil and gas wells, the suspension comprising polymer matrix particles suspended in an aqueous medium, each particle comprising a water-insoluble, porous, crosslinked polymer matrix, the polymer matrix comprising a polymer backbone and ionic functional groups covalently bonded to the backbone, the ionic functional groups being capable of selectively attracting and binding salt scale-forming ions when in contact with a liquid containing such ions.
 18. The suspension of claim 17 wherein the ionic functional groups are capable of selectively binding halite-forming ions.
 19. The suspension of claim 18 wherein the ionic functional groups are monovalent cationic groups capable of selectively binding halide ions.
 20. A method of inhibiting scale formation in an oil or gas well comprising: injecting polymer matrix particles into an oil or gas well, so that the polymer matrix particles come into contact with a liquid containing salt scale-forming ions, each polymer matrix particle comprising a water-insoluble, porous, crosslinked polymer matrix, the polymer matrix comprising a polymer backbone and ionic functional groups covalently bonded to the backbone, the ionic functional groups contacting the liquid and selectively attracting and binding the salt scale-forming ions.
 21. The method of claim 20 wherein the polymer matrix particles are injected in the form of a suspension of the particles in an aqueous medium.
 22. The method of claim 20 wherein the liquid containing the salt scale-forming ions is a brine.
 23. The method of claim 20 wherein the ionic functional groups selectively bind halite-forming ions.
 24. A method of inhibiting scale formation in an oil or gas well comprising: (a) injecting a suspension of polymer matrix particles into an oil or gas well, so that the polymer matrix particles come into contact with a liquid containing salt scale-forming ions, each polymer matrix particle comprising a water-insoluble, porous, crosslinked polymer matrix, the polymer matrix comprising a polymer backbone and ionic functional groups covalently bonded to the backbone, the ionic functional groups contacting the liquid and selectively attracting and binding the salt scale-forming ions; and then (b) separating the polymer matrix particles after they have bound the salt scale-forming ions.
 25. The method of claim 24, wherein the polymer matrix particles are separated by filtration or gravimetrically.
 26. The method of claim 24, further comprising regenerating the polymer matrix particles after they are separated by removing the bound salt scale-forming ions.
 27. The method of claim 26, wherein the polymer matrix particles are regenerated by using a controlled pH buffer to displace the salt scale-forming ions from the particles.
 28. The method of claim 24, wherein the liquid containing the salt scale-forming ions is a brine.
 29. A coating for application to an interior surface of an oil or gas well to inhibit scaling, the coating comprising: a continuous phase suitable for forming a coating on an interior surface of a well; and polymer matrix particles dispersed in the continuous phase for inhibiting scale formation, each particle comprising a water-insoluble, porous, crosslinked polymer matrix, the polymer matrix comprising a polymer backbone and ionic functional groups covalently bonded to the backbone, the ionic functional groups being capable of selectively attracting and binding salt scale-forming ions when in contact with a liquid containing such ions; and optionally, another treatment chemical useful in an oil or gas well. 